Heat transfer system

ABSTRACT

A heat transfer system is described for controlling the transfer of heat from a roof space into a living space of a building. The heat transfer unit ( 10 ) includes a flexible duct ( 14 ) and a ceiling vent ( 16 ) for transferring warm air from within the roof space ( 12 ) into a living space ( 18 ) below. An electric fan ( 20 ) located at the top end of the flexible duct ( 14 ) is arranged to draw warm air from the roof space ( 12 ) down through the duct ( 14 ) into the living space ( 18 ). A first temperature sensor ( 22 ) mounted adjacent the top end of the flexible duct ( 14 ) senses the temperature of the air within the roof space ( 12 ). A second temperature sensor ( 24 ) located in the room below senses the temperature of the air within the living space ( 18 ). An electronic controller ( 26 ) controls the operation of the electric fan ( 22 ) in response to temperature sensing signals from the first and second temperature sensors ( 22, 24 ) respectively. In particular, the controller ( 26 ) ensures that the electric fan ( 22 ) is only activated when the air temperature within the roof space exceeds the air temperature within the living space by a predetermined temperature difference. The unit ( 10 ) can also be employed in a cooling mode.

FIELD OF THE INVENTION

The present invention relates to a heat transfer apparatus and a methodfor controlling the transfer of heat from a roof space into a livingspace of a building and relates particularly, though not exclusively, toa heat transfer system that can also be employed to cool the livingspace.

BACKGROUND TO THE INVENTION

It is generally known that the temperature of air trapped in a roofspace, that is, the air held in the void between the roof claddingmaterial and the ceiling of a building, is considerably higher than theambient air temperature. The trapped air in the roof space becomesheated due to thermal energy from sunlight which is conducted throughthe roof tiles or other roof cladding material and re-radiated into theroof space. Some heating may also occur due to heat conducted throughthe ceiling from the living space below. The degree of heating of theair in the roof space to elevated temperatures is determined by a numberof factors, including the amount (intensity and duration) of sunlightthat the roof is exposed to, the ambient (outside) air temperature andthe extent of roof insulation.

Several prior art systems attempt to exploit the heat accumulated in theroof space for heating a living space below. For example, AU-B-32409/84discloses a Ventilator which can be used for recycling heated air from aroof cavity of a building or like structure back into a living/work areaof the structure. The ventilator assembly of AU-B-32409/84 may be sitedin either the roof or ceiling of the structure, and has an axial flowfan for generating a flow of heated air through the assembly. Atemperature sensing means 8, for example, a thermostat, may be providedto switch the fan on or off as required. The temperature sensing means 8may be located within the ventilator assembly or positioned remote fromthe assembly with interconnecting wiring. AU-A33942/93 discloses aventilation system designed specifically for ventilating warm air from aroof space for heating a living space below. The system of AU-A33942/93includes a vent 12 mounted in the ceiling 14 of a house and opening intothe living space below, and a ducting means 18 in the form of aconcertina ducting tube located in the roof space to providecommunication of air from a high point within the roof space to the vent12. An electric fan 20 forces air to flow through the ducting tube 18and vent 12 so that warm air can be ducted from the roof space into theliving space. The system of AU-A-33942/93 may include a thermostaticallycontrolled switching circuit adapted to switch automatically betweensummer and winter modes in response to changes in the ambient (exterior)air temperature. The electric fan is solar powered.

One of the disadvantages of these prior art systems is that they do notprovide any adequate means for controlling the transfer of air from theroof space at a sufficiently elevated temperature to ensure heating ofthe living space below. The present invention was developed with a viewto providing a heat transfer system that can ensure air is onlytransferred from the roof space when the temperature of the air in theroof space exceeds the temperature of the air in the living space by apredetermined amount.

SUMMARY OF THE INVENTION

Throughout this specification the term “comprising” is used inclusively,in the sense that there may be other features and/or steps included inthe invention not expressly defined or comprehended in the features orsteps subsequently defined or described. What such other features and/orsteps may include will be apparent from the specification read as awhole.

According to one aspect of the present invention there is provided aheat transfer apparatus for heating a living space in a building, theapparatus comprising:

air transfer means arranged within a roof space of the building fortransferring warm air from within the roof space into a living spacebelow;

an electric fan arranged to force air through said air transfer meansinto the living space;

a first temperature sensor within the roof space for sensing a first airtemperature within the roof space;

a second temperature sensor within the living space for sensing a secondair temperature within the living space; and

an electronic controller operatively connected to said electric fan andsaid first and second temperature sensors, and wherein said controllerensures that the electric fan is only activated when the first airtemperature exceeds the second air temperature by a first predeterminedtemperature difference and when the first air temperature exceeds apredetermined threshold temperature whereby, in use, warm airtransferred from the roof space is able to heat the living space.

More preferably the electric fan is only activated when the second airtemperature is below said preset room temperature by a secondpredetermined temperature difference. Advantageously said preset roomtemperature is adjustable by an occupant of the living space.

Preferably said controller also ensures that the electric fan is onlyactivated when the first air temperature exceeds a predeterminedthreshold temperature. More preferably the electric fan is onlyactivated when the first air temperature exceeds the predeterminedthreshold temperature by a third predetermined temperature difference.Typically said predetermined threshold temperature is set at between 20°C. and 25° C. More typically the predetermined threshold temperature isset at approximately 22.75° C.

According to another aspect of the present invention there is provided amethod for controlling the transfer of heat from a roof space into aliving space of a building using an electric fan to force warm air fromthe roof space of the building into the living space below, the methodcomprising:

sensing a first air temperature within the roof space;

sensing a second air temperature within the living space; and

activating said electric fan only when the first air temperature exceedsthe second air temperature by a first predetermined temperaturedifference and when the first air temperature exceeds a predeterminedthreshold temperature whereby, in use, warm air transferred from theroof space is able to heat the living space.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a more comprehensive understanding of the natureof the invention several embodiments of the heat transfer system willnow be described in detail, by way of example only, with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic diagram of a first embodiment of the heat transfersystem according to the invention in the form of a Do It Yourself (DIY)unit shown operating in a heating mode;

FIG. 2 is a schematic diagram of the DIY unit of FIG. 1 shown operatingin a cooling mode;

FIGS. 3 and 4 illustrate graphically operation of the DIY unit of FIG. 1in heating and cooling modes respectively;

FIG. 5 is a schematic diagram of a heat transfer system that employs aplurality of DIY units similar to that of FIG. 1 in a MASTER/SLAVEconfiguration;

FIG. 6 is a schematic diagram of a second embodiment of the heattransfer system employed in conjunction with a conventional airconditioning system;

FIG. 7 is a schematic diagram of a third embodiment of the heat transfersystem employed in conjunction with a conventional air conditioningsystem;

FIG. 8 is a schematic plan view of a fourth embodiment of the heattransfer system employed in a large building such as a shopping centre;

FIG. 9 is a schematic side elevation of the heat transfer system of FIG.8; and,

FIG. 10 is a plan view of a differential damper arrangement that can beused in connection with the heat transfer system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the heat transfer system according to the presentinvention as shown in FIGS. 1 and 2 is in the form of a Do It Yourself(DIY) unit 10 which can be installed in a roof space 12 of a building,such as a residential house, by the home handyman. The unit 10 comprisesa flexible duct 14 and a ceiling vent 16 for transferring warm air fromwithin the roof space 12 into a living space 18 below. An electric fan20 located at the top end of the flexible duct 14 is arranged to drawwarm air from the roof space 12 down through the duct 14 and vent 16into the living space 18. An axial fan 20 is illustrated, however anysuitable electric fan may be employed. The heat transfer unit 10 furthercomprises a first temperature sensor 22 typically mounted on the side ofthe flexible duct 14 adjacent the top end thereof, for sensing thetemperature of the air (T3) within the roof space 12. A secondtemperature sensor 24, which is typically located on a wall in the roombelow, senses the temperature of the air (T1) within the living space18. Ceiling vent 16 or duct 14 may optionally include an air filter tofilter out any dust or other air-borne particles.

The heat transfer unit 10 further comprises an electronic controller 26,which in this embodiment is located within a housing of the ceiling vent16 for convenience. Controller 26 controls the operation of the electricfan 22 in response to temperature sensing signals from the first andsecond temperature sensors 22, 24 respectively. In this connection, thecontroller 26 includes an analogue to digital converter (ADC) forconverting the analogue sensing signals from the sensors 22, 24 into adigital format for processing by the processor unit of the controller26. Typically electronic controller 26 is a microprocessor-basedcontroller, although any suitable electronic controller may be employed,such as a programmable logic controller (PLC), which is capable ofcontrolling operation of the heat transfer apparatus according to thefollowing control strategy.

Through trial and experimentation, the inventor has found that unlessthere is a significant temperature difference between the airtemperature within the roof space and the air temperature in the livingspace, air transferred from the roof space will be ineffective inheating the living space. Furthermore, unless the temperature in theroof space exceeds a predetermined threshold temperature, transferringair from the roof space will not create the desired heating effect.Indeed, if the air being transferred into the living space is at atemperature below the predetermined threshold temperature, the movementof air can have a cooling effect on the occupants, rather than a warmingeffect. Typically, the predetermined air temperature threshold is setbetween approximately 20° C. and 25° C., most preferably atapproximately 22.75° C.

The above heating control strategy can be implemented in the electroniccontroller using the following control logic:

Heating On If T1 < (S/P-P2) (With P2 Differential) . . . (1) And T3 >(T1 + P1) (With P5 Differential) . . . (2) And T3 > (P3 + P4) (With P4Differential) . . . (3) Then R2 energises Heating Off If the above isnot true Then R2 de-energises

Where,

T1 = Room Temperature T2 = Outside (Ambient) Air Temperature T3 = RoofSpace Temperature S/P = Room Temperature Set Point - AdjustablePotentiometer P1 = Temperature Differential (initially set to 2.5K) P2 =Temperature Differential (initially set to 0.25K) P3 = ThresholdTemperature - Heating Mode (initially set to 22.75° C.) P4 = TemperatureDifferential (initially set to 0.50K) P5 = Temperature Differential(Heating Fan) (initially set to 0.50K) P6 = Temperature Differential(Cooling Fan) (initially set to 0.50K) R1 = Cooling Fan Start Relay R2 =Heating Fan Start Relay

Each of the parameters P1 to P6 is software adjustable within thecontroller 26. Each of the above logical conditions operates with itsown additional temperature differential. Thus, for example, condition(2) operates with a P5 temperature differential. This means that ifcondition (2) is satisfied, which means that the electric fan forheating has been activated, the electric fan will not be de-activateduntil the roof space temperature (T3) drops below (T1+P1) by at least0.5K (P5) assuming conditions (1) and (3) remain true. Without anappropriate temperature differential (P5) there is a danger that thecontroller would continue to activate the heating fan as the airtemperature (T3) in the roof space cools therefore driving the airtemperature in the living space (T1) downwards. This is showngraphically in FIG. 3 where it appears that at about 6.30 pm the coolerair from the roof space started to drive the air temperature in theliving space downwards. In that case, P5 was set at 2.5K (P5=P1) whichmeant the controller would not shut off the heating fan unless T3 fellbelow T1 which is difficult to achieve and not desirable.

In FIG. 3, the operation of the heat transfer unit in a heating mode isillustrated graphically over a fourteen hour period from approximately8.00 am to 10.00 pm. FIG. 3 graphs the air temperature in a room withthe heat transfer unit installed (room 1), the air temperature inanother room with no heat transfer unit installed (room 2) forcomparison, the outside (ambient) temperature and the roof spacetemperature. At approximately 10.00 am the temperature in the roof spacestarted to climb above the ambient temperature and the room temperature,climbing to a peak of approximately 34° C. at 3.00 pm. The roomtemperature set point (S/P) was set at 24° C. and the temperature limitlockout threshold temperature (P3) was set at 22.75° C. It will be seenthat conditions (1), (2) and (3) were all satisfied at approximately11.30 am at which point the controller activated the heating fan.Thereafter, the temperature in room 1 started to climb as warm air fromthe roof space was transferred into room 1 by the heat transfer unit. Atabout 2.00 pm the temperature in room 1 reached 24° C. (S/P) at whichpoint the controller deactivated the heating fan. For the remainder ofthe day the heat transfer unit continued to cycle utilising the P2differential to maintain the air temperature in the room around thepreset room temperature of 24° C. (S/P) in accordance with the abovecontrol algorithm, until the roof space temperature fell below 22.75° C.(P3) at approximately 7.30 pm. Thereafter, the controller deactivatedthe heating fan.

The electric fans 20,30 may be variable speed fans capable of operatingat two or more speeds. In that case, the controller 26 may be programmedto adjust the speed of the fans in accordance with changes intemperature. For example, in the heating mode, if the temperature in theroof space (T3) is higher than the room temperature (T1), but stillbelow the threshold temperature (P3), the electric fan 20 may beswitched ON at low speed. However, once the roof space temperatureexceeds the threshold temperature (P3), the controller will be switchedto a higher speed. The reverse sequence could occur as the temperaturein the roof space starts to cool. The controller 26 may also include atime clock to automatically switch the unit on or off after apredetermined time interval or at preprogrammed times.

The heat transfer unit 10 can also be made to operate in a cooling modeas illustrated in FIG. 2. In this mode, the heat transfer unit alsorequires a third temperature sensor located outside the building forsensing a third air temperature (T2) corresponding to the ambient oroutside air temperature. The third temperature sensor 28 is preferablylocated under the eaves of the roof away from the walls of the buildingwhich may have become heated due to sunlight. The heat transfer unit 10also preferably further comprises a second electric fan 30 used in thecooling mode for transferring warm air from within the living space intothe roof space above. For this purpose, the cooling fan 30 is preferablylocated at the lower end of the duct 14 adjacent the ceiling vent 16. Inan alternative embodiment, a single reversible electric fan could beemployed at any location in place of the first and second fans 20, 30for use in both heating and cooling modes. However, the non-reversiblefans employed are very low cost and easily replaceable by the homehandyman. Furthermore, the use of two electric fans located atrespective ends of the flexible duct 14 has been found to work well inpractice, and has the further advantage of inhibiting a thermo-syphoningeffect during the winter months, when hot air may be syphoned up throughthe ceiling vent 16 due to convection when the heat transfer unit is notin operation.

In the cooling mode, the electronic controller controls the operation ofthe cooling fan 30 according to the following control strategy:

Cooling On If T1 > (S/P + P2) (With P2 Differential) . . . (4) And T2 <(T1 − P1) (With P6 Differential) . . . (5) Then R1 energises Cooling OffIf the above is not true Then R1 de-energises

In the cooling mode, the heat transfer unit 10 is most effective atnight when the ambient air temperature (T2) is likely to fall below theinside room temperature (T1). Under these conditions, provided that theroom temperature exceeds the preset room temperature (S/P) by the secondpredetermined temperature differential, the cooling fan 30 is activatedto transfer warm air from within the living space 18 into the roof space12. For this purpose, a window 32 in the room below must be opened inorder to allow cool ambient air to be drawn into the living space 18 toreplace the warm air being transferred into the roof space 12. The warmair being transferred into the roof space is typically cooler than theair already in the roof space. Therefore this has the additional benefitof cooling the air in the roof space, which also helps to reduce thetemperature in the living space below.

FIG. 4 illustrates graphically the operation of the heat transfer unit10 in a cooling mode during a nine hour period from approximately 9.15pm to 7.30 am. Once again, the temperature in another room without aheat transfer unit is shown for comparison. It can be seen that at 9.15pm, the outside air temperature had already fallen to well below theinside room temperature, and therefore the heat transfer unit commencedoperation immediately in the cooling mode. As can be seen in FIG. 4, thetemperature in the room cooled with a heat transfer unit was loweredsignificantly below that of the room without heat transfer unitthroughout the night from approximately 11.00 pm onwards.

As a DIY unit, the heat transfer unit 10 is designed to be sold as a kitand installed with the minimum amount of work and alterations. A holewill need to be cut through the ceiling in order to receive the ceilingvent 16 with the duct 14 attached thereto. Advantageously, the flexibleduct 14 is of a concertina-type construction which enables the entireunit to be packaged within a carton of approximately 350 mm² by 350 mmhigh. The flexible duct 14 extends up to approximately 1.5 metres inlength to accommodate varying ceiling to roof distances and to enablethe warmer air near the top of the roof space to be transferred into theliving space in the heating mode. The complete kit, which includes theduct, fans, controller and sensor cables is very compact when packagedand weighs approximately 5 kilograms for economical freight and ease ofhandling.

The unit is self-contained with all controls typically mounted on a rimof the ceiling vent 16. These controls typically include a switch forselecting heating or cooling mode and a control knob 34 for manuallyadjusting the preset room temperature (S/P). Alternatively, a remotecontrol may be provided which communicates with the controller 26 viaradio frequency (RF) or infrared (IR) transmission. Advantageously, theremote control may be wall-mounted and may incorporate the secondtemperature sensor 24 for sensing the temperature within the livingspace 18. A home handyman can easily carry out the entire installationin approximately 2 hours, except for the provision of a non-switchedpower outlet 36 above the ceiling adjacent the location of the heattransfer unit 10 for supplying power thereto.

Each DIY heat transfer unit 10 is capable of heating or cooling an areaof up to approximately 40 square metres. If desired, a plurality of suchheat transfer units 10 may be installed in selected rooms throughout thebuilding to provide uniform heating/cooling throughout the building.FIG. 5 illustrates a heat transfer system which employs a master heattransfer unit 40 with a plurality of slave heat transfer units 42connected thereto. The master unit 40 is similar to the heat transferunit 10 of FIGS. 1 and 2 in that it incorporates an electroniccontroller for controlling operation of the heat transfer system.However, each of the slave units 42 does not require an electroniccontroller, as it is controlled by the controller of the master unit 40.Optionally, each slave unit 42 may be provided with its own roomtemperature sensor for sensing the air temperature in the living spacebelow each slave unit 42. In this way, the electronic controller in themaster unit 40 is able to monitor the air temperature throughout thebuilding and activate a particular slave unit 42 to provide selectiveheating/cooling in response to changes in the room temperature. However,more typically only the master unit 40 is provided with a roomtemperature sensor 44, which is used by the master unit 40 to controlthe operation of all of the slave units 42 simultaneously. Each of theseslave units 42 may be hardwired to the master unit 40 as shown in FIG.5. Alternatively, wireless communication links may be employed betweenthe slave units 42 and master unit 40 using low-power RF transmission.

When using a single heat transfer unit 10 in the heating mode it is notusually necessary to provide any additional ventilation in the livingspace, as the cooler air being displaced by warmer air from the roofspace escapes under doors and through other leakage gaps. However, whenusing multiple heat transfer outlets as shown in FIGS. 5, 6 and 7 it maybe necessary to open one or more doors or windows to avoidpressurisation of the living space and allow efficient operation.

A larger version of the DIY heat transfer unit may be provided forheating or cooling larger areas. For example, the unit may incorporate amore powerful fan capable of transferring a greater volume of air fromthe roof space into the living space below. Such an enlarged DIY unitmay be fitted into an existing manhole cover, of the kind that is oftenfound in the hallway ceiling or other central location of a house foraccess to the roof space. In this way the need to cut a new hole in theceiling can be avoided and the unit is more easily removed.

The heat transfer system in accordance with the present invention may beemployed in conjunction with and/or incorporated within a conventionalair conditioning system at the time of manufacture or installation. Inthis connection, the heat transfer system may be retrofitted to anexisting air conditioner which has already been installed in a building.One of the advantages of such an arrangement is that the heat transfersystem can make use of the existing ducting provided for the airconditioner.

FIG. 6 illustrates a second embodiment of the heat transfer system 50which utilises the ducting system for an external air conditioner (notshown). The external air conditioner may, for example, be an evaporativeair conditioner of the kind which is mounted on the roof of a building.The heat transfer unit 50 includes a warm air duct 52 which is connectedto an existing duct 54 of the air conditioner connected to a ceilingvent 56 and a plurality of other outlets via branching ducts 57. Thewarm air duct 52 is connected to the air conditioner duct 54 near anupper region of the roof space 12 where the warmer air tends toaccumulate. Advantageously the warm air duct 52 extends for somedistance through the upper region of the roof space 12 and is providedwith a plurality of inlet ports 55 facing downwards at spaced intervalsalong its length. Warm air is drawn in via inlet ports 55 with minimumrisk of dust entering the warm air duct 52. A moveable diverter ordamper 58 can be moved between a first position (as shown) in which theduct 52 opens into the air conditioner duct 54 to allow the transfer ofwarm air from within the roof space 12 into the living space 18 below,and a second position (shown in broken outline) in which the duct 52 isclosed and cool air from the air conditioner can be transferred via theair conditioner duct 54 into one or more living spaces 18 below. Damper58 may be manually moveable, or may be automatically moveable when theheat transfer system is switched from a heating mode to a cooling modeor vice versa. Separate dampers may be provided in the air conditionerduct 54 and the warm air duct 52 if preferred.

An electric fan 60 is provided within the warm air duct 52 arranged toforce air through the air conditioner duct 54 into the living spacebelow. Although the electric fan 60 as shown in FIG. 6 is an axial fan,any suitable electric fan may be employed. A large drum fan may berequired to transfer the volume of air from the roof space via the airconditioner ducting system throughout the building. A first temperaturesensor 62 provided adjacent the inlet ports 55 of the duct 52 senses theair temperature within the roof space 12, and a second temperaturesensor 64 senses the air temperature within the living space 18. Boththe first and second sensors 62, 64 are connected to an electroniccontroller 66 which controls the operation of the electric fan 60 andpossibly also the damper 58. Interconnecting wires have been omitted forclarity. Advantageously, the second temperature sensor 64 may beincorporated in a remote control of the air conditioning unit which isalso designed to communicate with the electronic controller 66 via RF orIR transmission.

The electronic controller 66 may be fully integrated into the controlsystem for the air conditioner, or may be separate as a stand-aloneunit. In this embodiment, the heat transfer apparatus 50 does notoperate in a cooling mode, as the air conditioner can be employed toprovide cooling when required. In other respects, operation of the heattransfer apparatus 50 is similar to that of the heat transfer unit 10described above.

In some applications, it may be possible to utilise the same electricfan for both the external air conditioner and the heat transferapparatus. In such an arrangement, an electric fan is located in theduct 54 below the damper 58 so that it draws air down from the airconditioner in the cooling mode and down from the roof space via warmair duct 52 in the heating mode. The arrangement of FIG. 6 has thefurther advantage that the damper 58 prevents a downdraft of cold airfrom outside during cooler weather in the heating mode.

With conventional evaporative cooling systems it is generally essentialto have at least one window or door open in cooling mode so that thewarm air in the living space can be displaced by the cooled air enteringvia the air conditioner duct 54. However, it is also known to provide asecurity vent 59 in the ceiling of the building so that the evaporativecooler can be operated at night, or when the building is unoccupied,without compromising security. Security vent 59 is a one-way vent thatonly opens once the air within the living space 18 becomes pressurised,to allow the warmer air near the ceiling to be vented into the roofspace. The security vent 59 can be used in a similar manner with theheat transfer system 50 operating in the heating mode. The security vent59 needs to be positioned sufficiently distant from the warm air duct 52to prevent short-circuiting. If all windows and doors are closed, warmair being transferred into the living space 18 will eventuallypressurise the living space sufficiently to open the security vent 59.The air near the ceiling will then be vented into the roof space whereit can be reheated before being recycled through the heat transfersystem. This may improve the performance of the heat transfer system,particularly when the outside air temperature is cooler than the airtemperature in the living space, as the air replaced in the roof spacethen requires less heating.

In FIG. 7 a third embodiment of the heat transfer system in accordancewith the invention is illustrated this time utilising a ducting systemand fan for an internal air conditioner. In the heat transfer apparatus70 of this embodiment, air transfer means in the form of airconditioning ducting 72 is employed in conjunction with a warm air duct74 for transferring warm air from within the roof space 12 to one ormore living spaces 18 within the building. The illustrated embodimentemploys a reverse cycle air conditioner, for example, of the splitsystem kind which has a fan 76 located within the roof space and areturn air duct 78 for drawing air back up from the living space 18 forcooling or heating as required. The warm air duct 74 is located adjacentthe return air duct 78 and is provided with a damper or diverter 80 forclosing off the return air duct 78 (as shown) in the heating mode of theheat transfer apparatus 70. In the heating mode, the heat transferapparatus 70 employs the air conditioner fan 76 to force air through theducting 72 into one or more living spaces 18 below.

A first temperature sensor 82 is provided adjacent the inlet of the warmair duct 74 for sensing the air temperature within the roof space 12 anda second temperature sensor 84 is provided within the room below forsensing the air temperature within the living space 18. Both temperaturesensors 82, 84 are connected to an electronic controller 86 whichcontrols the operation of the air conditioner fan 76 in the heating modeof the heat transfer apparatus 70. Controller 86 may be incorporated inthe control system of the air conditioner if desired. Controller 86 isprogrammed to activate the air conditioner fan 76 only when the airtemperature within the roof space 12 exceeds the air temperature withinthe living space 18 by a predetermined temperature differential so thatwarm air transferred from the roof space is able to heat the livingspace below. Operation of the heat transfer apparatus 70 is similar tothat of the previous embodiments and will not be described in detailagain.

If desired, the heat transfer system 70 of FIG. 7 may optionally befitted with a second electric fan located in the warm air duct 74, toenable the system to operate in a cooling mode. This may provide a lowcost alternative to switching on the air conditioner, especially atnight time. The second electric fan is designed to draw warm air fromwithin the living space 18 up through ducting 72 and into the roof space12 through duct 74. Damper 80 is left in the same position as in theheating mode, and air conditioner fan 76 is left off. Cool air fromoutside is allowed to flow in through window 88 to replace the warm airdrawn up into the roof space.

FIG. 10 illustrates a further modification which may be incorporated inthe heat transfer system in accordance with the invention which allowssimultaneous cooling of the roof space in the cooling mode. For example,the arrangement of FIG. 10 may be employed with the heat transfer systemof FIG. 6. The arrangement of FIG. 10 includes an electric fan 90 fordrawing warm air from the roof space into a warm air duct 92 (similar tofan 60 and duct 52 in FIG. 6). A differential damper 94 is provided forallowing the warm air for the roof space to be directed into either anair conditioner duct 95 or an eaves duct 96 as required. Differentialdamper 94 includes a first damper 97 for opening and closing access fromthe warm air duct 92 to the air conditioning duct 95, and a seconddamper 98 for opening and closing access from the warm air duct 92 tothe eaves duct 96. The first and second dampers 97,98 are mounted on acommon spindle but at 180° with respect to each other. Thus, when one ofthe dampers is opened the other will be closed, and vice versa. Asuitable actuator, for example a small stepper motor may be provided forpivoting the differential damper 94 through 90° in a clockwise directionor an anti-clockwise direction as required.

In the heating mode differential damper 94 will be positioned so thatthe first damper 97 is open to allow warm air to be forced by theelectric fan 90 into the air conditioning duct 95. However, in a coolingmode differential damper 94 will be repositioned so that the firstdamper 97 is closed and the second damper 98 is in the open position (asshown in FIG. 10). In this mode, the electric fan 90 can be operated toexhaust warm air from the roof space to the exterior of the buildingthrough the eaves duct 96. In this way, not only is the living spacebelow being cooled by the air conditioning system via duct 95, but theroof space above is also being cooled by exhausting the accumulated warmair to atmosphere. Reducing the temperature of the roof space candramatically improve the cooling of the living space as it minimises thereradiation of heat from the roof space through the ceiling into theliving space.

The heat transfer system of the present invention is not limited todomestic applications, but may also be employed in large commercialenvironments such as shopping centres and industrial buildings. FIGS. 8and 9 illustrate a fourth embodiment of the heat transfer system whichhas been installed in a large commercial building for operation inconjunction with a conventional air conditioning system. In the heattransfer apparatus 100 of this embodiment, air transfer means in theform of a warm air inlet manifold 102 is employed in conjunction withthe existing ducting 103 for the air conditioning system fortransferring warm air from within the roof space 104 into the livingspace 106 within the building. An air handler unit 108 of theconventional air conditioning system includes one or more large fanswhich are used to force air through the air conditioning ducting intothe living space 106 below. The warm air inlet manifold 102 is providedwith a plurality of inlet ports 107 provided at spaced intervals alongits length for drawing warm air from the roof space 104 into the airhandling unit 108. In this way, the warm air within the whole volume ofthe roof space can be employed for heating the living space below.

A return air manifold 110 is provided within the roof space 104 somedistance from the inlet manifold 107, and preferably at the other end ofthe building. Return air is drawn up from the living space 106 belowthrough a return air grille 112 which covers a return air duct thatfeeds into the return air manifold 110. A plurality of outlet ports 114are provided at spaced intervals along the length of the return airmanifold 110 for returning the air into the roof space 104. The returnair gently wafts through the roof space 104 in which it is heated bysolar radiation before being drawn into the warm air inlet manifold 102.

One or more first air temperature sensors 116 may be provided adjacentthe warm air inlet manifold 102 for sensing the air temperature withinthe roof space 104. One or more second air temperature sensors 118 areprovided within the room or rooms below for sensing the air temperaturewithin the living space 106. Both temperature sensors 116,118 areconnected to an electronic controller 120 which controls the operationof the air handling unit 108 in the heating mode of the heat transferapparatus 100. Controller 120 may be incorporated in the control systemof the air conditioning system if desired. Controller 120 is programmedto activate the transfer of warm air from the roof space through the airhandler unit 108 only when the air temperature within the roof space 104exceeds the air temperature within the living space 106 by apredetermined temperature differential so that warm air transferred fromthe roof space is able to heat the living space below. It will beunderstood that various damper arrangements will be required to redirectthe flow of air from various sources through the air handling unit 108and ducting in different operational modes of the air conditioningsystem. Operation of the heat transfer apparatus 100 is similar to thatof the previous embodiments and will not be described in detail again.

Now that several embodiments of the heat transfer system have beendescribed in detail, it will be apparent that it provides a number ofadvantages including the following:

(i) it can provide low-cost and environmentally friendly heating and/orcooling of a living space by utilising solar heated warm air within theroof space and/or cool air from outside;

(ii) the use of temperature sensors and a controller ensures that theair temperature within the living space can be maintained close to apreset room temperature whenever possible;

(iii) in the heating mode it ensures that warm air is only transferredfrom the roof space when the air temperature in the living space is lessthan a set point temperature by a predetermined amount, and when thetemperature of the air in the roof space exceeds a threshold temperatureand the temperature of the air in the living space by a predeterminedamount;

(iv) in the cooling mode it ensures that cool air is only transferredfrom the outside when the air temperature in the living space exceedsthe outside air temperature and the set point temperature bypredetermined amounts;

(v) in the cooling mode, the transfer of relatively cooler air into theroof space also helps to reduce the temperature in the living spacebelow;

(vi) it is low cost to manufacture and easy to install and operate;

(vii) it can be incorporated or retrofitted in conventional evaporativeand refrigerated air conditioning systems;

(viii) in the Do It Yourself (DIY) it is ideal for the home handyman andis readily expanded to suit commercial environments; and,

(ix) it provides a low cost method of utilising the thermal mass of thebuilding, with the added option of raising the set point temperatureabove a comfort level so as to heat the interior of the buildingthroughout the day, which provides reradiated heating during the night.

Numerous variations and modifications will suggest themselves to personsskilled in the air conditioning arts, in addition to those alreadydescribed, without departing from the basic inventive concepts. Forexample, each of the temperature sensors may be fitted with a low powerRF transmitter for transmitting a temperature sensing signal to theelectronic controller thus obviating the need for installation ofconnecting cables. All such variations and modifications are to beconsidered within the scope of the present invention, the nature ofwhich is to be determined from the foregoing description and theaccompanying claims.

What is claimed is:
 1. A heat transfer apparatus for heating a livingspace in a building, the apparatus comprising: air transfer meansarranged within a roof space of the building for transferring warm airfrom within the roof space into a living space below; an electric fanarranged to force air through said air transfer means into the livingspace; a first temperature sensor within the roof space for sensing afirst air temperature within the roof space; a second temperature sensorwithin the living space for sensing a second air temperature within theliving space; and an electronic controller operatively connected to saidelectric fan and said first and second temperature sensors, and whereinsaid controller ensures that the electric fan is only activated when thefirst air temperature exceeds the second air temperature by a firstpredetermined temperature difference and when the first air temperatureexceeds a predetermined threshold temperature, wherein saidpredetermined threshold temperature is selected to ensure that movementof the air from the roof space does not have a cooling effect on anoccupant of the living space whereby, in use, warm air transferred fromthe roof space is able to heat the living space.
 2. A heat transferapparatus as defined in claim 1, wherein said controller also ensuresthat the electric fan is only activated when the second air temperatureis below a preset room temperature.
 3. A heat transfer apparatus asdefined in claim 2, wherein the electric fan is only activated when thesecond air temperature is below said preset room temperature by a secondpredetermined temperature difference.
 4. A heat transfer apparatus asdefined in claim 3, wherein said preset room temperature is adjustableby an occupant of the living space.
 5. A heat transfer apparatus asdefined in claim 1, wherein the electric fan is only activated when thefirst air temperature exceeds the predetermined threshold temperature bya third predetermined temperature difference.
 6. A heat transferapparatus as defined in claim 5, wherein said predetermined thresholdtemperature is set at between 20° C. and 25° C.
 7. A heat transferapparatus as defined in claim 6, wherein the predetermined thresholdtemperature is set at approximately 22.75° C.
 8. A method forcontrolling the transfer of heat from a roof space into a living spaceof a building using an electric fan to force warm air from the roofspace of the building into the living space below, the methodcomprising: sensing a first air temperature within the roof space;sensing a second air temperature within the living space; and activatingsaid electric fan only when the first air temperature exceeds the secondair temperature by a first predetermined temperature difference and whenthe first air temperature exceeds a predetermined threshold temperature,wherein said predetermined threshold temperature is selected to ensurethat movement of the air from the roof space does not have a coolingeffect on an occupant of the living space whereby, in use, warm airtransferred from the roof space is able to heat the living space.
 9. Amethod for controlling transfer of heat as defined in claim 8, whereinthe electric fan is only activated when the first air temperatureexceeds the predetermined threshold temperature by a secondpredetermined temperature difference.
 10. A method for controllingtransfer of heat as defined in claim 9, wherein said predeterminedthreshold temperature is set at between 20° C. and 25° C.
 11. A methodfor controlling transfer of heat as defined in claim 10, wherein thepredetermined threshold temperature is set at approximately 22.75° C.12. A method for controlling transfer of heat as defined in claim 8,wherein the electric fan is only activated when the second airtemperature is below a preset room temperature.
 13. A method forcontrolling transfer of heat as defined in claim 12, wherein theelectric fan is only activated when the second air temperature is belowsaid preset room temperature by a third predetermined temperaturedifference.
 14. A method for controlling transfer of heat as defined inclaim 13, wherein said preset room temperature is adjustable by anoccupant of the living space.